Such spring washers are used for the axial preload of anti-friction bearings of a bearing block. Such a bearing block commonly comprises a stationary component, a shaft and an anti-friction bearing that is located in between. An outer bearing ring of the anti-friction bearing is fixed to the aforementioned component, and an inner bearing ring of the anti-friction bearing is fixed to the shaft.
It is generally known from the prior art to preload anti-friction bearings axially by means of spring washers or conventional coil springs. The axial preload is necessary for numerous applications, since in the case of anti-friction bearings, especially radially grooved ball bearings, a radial play occurs between the balls and the outer and inner bearing ring. This play results in increased vibrations, especially at high rotational speeds. Because of this the bearing runs unsteadily, and in case of longer operations fretting wear is likely to occur due to the friction between the balls and the bearing rings. Thanks to axial preload this radial play can be avoided, since the bearing balls are in contact with the bearing rings due to the axial preload with a predefined contact angle between the ball's surface and the running track.
The axial preload by means of conventional compression coil springs has the disadvantage that compression coil springs are comparatively long and therefore require a large installation space.
Therefore, components which are referred to as spring washers have already been used for a long time for axial preloading. From EP 0303147 A1 a corrugated spring washer is known which is produced as stamped-bent part in one piece and basically comprises two concentrically arranged rings. The inner ring is connected to the outer ring by means of several connection rods. The inner ring is flat, whereas the outer ring is corrugated so it describes a sinusoidal curve alongside its perimeter in axial direction. The spring force is primarily produced due to the corrugated shape of the outer ring. Through the impact of axially applied force the corrugated outer ring is pressed flat so at maximum load the ring would be in-plane. Those corrugated spring washers have the disadvantage that in the course of time creeping occurs which is caused by a plastic deformation of the corrugated outer ring. This means that the spring force, which is produced by the corrugated spring washer, decreases over the course of time at the same rate of deflection.
CH 240887 describes a spring washer for the axial preload of an anti-friction bearing. The spring washer mainly consists of an outer ring from which inwardly directed cantilevered rods protrude, which are equally spread along the perimeter of the spring washer. Moreover, the cantilevered rods are bent up in axial direction and are pressed flat into the plane of the outer ring when exposed to axial load.
DE 10214276 A1 describes another spring washer, which is from its principal of operation similar to the spring washer from CH 240887. Here however, the continuous ring is located inside, whereas the resilient cantilevered rods of the inner ring protrude outwards. The resilient rods are also bent up axially.
DE 29801110 U1 presents a spring washer which is formed—similar to a coil spring—to a cone-shaped helical sheet metal strip which connects an outer ring to an inner ring. Since the outer and inner rings are only connected through a single spirally shaped rod, the rings are not solidly concentrically positioned and the rings can easily be tilted against one another. A spring force that is equally acting on the entire perimeter is impossible to achieve with this spring washer.
A spring washer of the type mentioned in the beginning is finally known from DE 102004041074 A1. It comprises an outer and inner ring which are concentrically arranged and connected through three resilient connection rods. The outer and inner ring have an axial offset and are therefore not in-plane. These three resilient connection rods are slightly spiral shaped in order to exhibit an adequate length for the intended spring effect. A similar spring washer of this type is described by WO 02/092244 A1.
In order to extend the length of the resilient connection rods U.S. Pat. No. 4,792,708 suggests implementing the connection rods in a snake shape. Each connection rod runs back and forth between the inner and outer ring alongside a specific part of the perimeter of the spring washer in a snake shape.
With the state of the art spring washers of the type mentioned in the beginning, the problem occurs that the length of the connection rods between the inner and outer ring of the spring washer cannot be altered lengthwise as required in order to achieve the requested spring effect, if there is only little installation space available especially in radial direction. The snake shaped version of the connection rods known from U.S. Pat. No. 4,792,708, for instance, leads to the fact that the inner ring cannot be kept stable and concentric to the outer ring. Therefore the object of the present invention is to improve the state of the art spring washers and especially indicate a possibility to extend the effective length of the resilient elements in order to achieve the requested spring effect without risking the stable and coaxial connection between the inner and outer ring. Moreover, the object of the present invention is to propose a spring washer with the smallest installation space possible and minor deviation of the spring characteristics in the case of full deflection, which on top of that can be manufactured cost-effectively.